Overview of sound measurement and related products



Structure of the condenser-type microphone

Microphone can basically divided into three types, electrodynamic-type, condenser-type, and piezoelectric-type according to its conversion methods. The electrodynamic-type has well-established demand in the music world, and the piezoelectric-type is mainly used for a microphone of a low frequency sound level meter. Condenser-type is popularly used as measurement microphone. It features not only to be downsized with ease, but also to have flat frequency responses over a wide range of frequency, and provides markedly high stability. Condenser-type microphone is available in two types, bias-type and back electret-type. The difference is the way to apply the DC voltage. Bias-type is required to supply DC voltage from external. Back electret-type is affixed permanently electrically polarized polymer film to the surface of backplate in place of applying voltage. Generally, bias-type is much more sensitive and stable than back electret-type.

Operating principle of the Sound Intensity Probe

Sound intensity is a measure of the "flow of energy passing through a unit area per unit time" and its measurement unit is W/m2. The sound intensity microphone probe is designed to capture sound intensity together with the unit direction of flow as a vector quantity. This is achieved by incorporating more than one microphone in a probe to measure the sound energy flow. Conventional microphones can measure sound pressure (unit: Pa), which represents sound intensity as a specific place (one point), but can measure the direction of flow. The sound intensity microphone is therefore used for sound source probing and for measuring sound power. Ono Sokki produces two types of sound intensity microphones—a single-axis type (model MI-6410) in which two pairs of sound pressure microphones are arranged close to each other in a straight line; and a three-dimensional type (model MI-6420) unique to Ono Sokki, in which four microphones are placed in each apex of a regular tetrahedron.

Please read "Sound and sensors" in "Ono Sokki Technical Report" for more details




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